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The role of cattle and other ruminants in reducing agriculture’s carbon footprint in North America

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The role of ruminants in reducing agriculture’s carbon footprint in North America (pdf)

MARCH/APRIL 2016 —VOL. 71, NO. 2 Teague et al  doi:10.2489/jswc.71.2.156
http://www.jswconline.org/content/71/2/156.full.pdf

W.R. Teague, S. Apfelbaum, R. Lal, U.P. Kreuter, J. Rowntree, C.A. Davies, R. Conser, M. Rasmussen, J. Hatfield, T. Wang, F. Wang, and P. Byck

Abstract: Owing to the methane (CH4 ) produced by rumen fermentation, ruminants are a source of greenhouse gas (GHG) and are perceived as a problem. We propose that with appropriate regenerative crop and grazing management, ruminants not only reduce overall GHG emissions, but also facilitate provision of essential ecosystem services, increase soil carbon (C) sequestration, and reduce environmental damage. We tested our hypothesis by examining biophysical impacts and the magnitude of all GHG emissions from key agricultural production activities, including comparisons of arable- and pastoral-based agroecosystems. Our assessment shows that globally, GHG emissions from domestic ruminants represent 11.6% (1.58 Gt C y-1) of total anthropogenic emissions, while cropping and soil-associated emissions contribute 13.7% (1.86 Gt C y-1). The primary source is soil erosion (1 Gt C y-1), which in the United States alone is estimated at 1.72 Gt of soil y-1. Permanent cover of forage plants is highly effective in reducing soil erosion, and ruminants consuming only grazed forages under appropriate management result in more C sequestration than emissions. Incorporating forages and ruminants into regeneratively managed agroecosystems can elevate soil organic C, improve soil ecological function by minimizing the damage of tillage and inorganic fertilizers and biocides, and enhance biodiversity and wildlife habitat. We conclude that to ensure long-term sustainability and ecological resilience of agroecosystems, agricultural production should be guided by policies and regenerative management protocols that include ruminant grazing. Collectively, conservation agriculture supports ecologically healthy, resilient agroecosystems and simultaneously mitigates large quantities of anthropogenic GHG emissions.

From the Text:

Historically, many rangelands have been subjected to increasingly heavy continuous grazing (CG) by livestock. This management approach, which allows sustained access to plants by grazing ruminants without an opportunity for recovery between grazing events, has been documented as contributing to serious negative effects, such as depletion of root biomass and carbohydrate reserves in selectively grazed plants and reduction in aboveground biomass productivity. Other negative effects of poor grazing management include impoverished herbaceous plant communities, more bare ground, lower SOC reserves, and increased soil erosion and compaction (Janzen 2010; Teague et al. 2013). At landscape scales these changes have contributed to lower surface water infiltration, increased runoff and downstream flooding, and reductions in water quality (Janzen 2010; Teague et al. 2013). As with tillage agriculture, the sediments from eroded grassland soils also emit GHG when organic matter in sediments enters anaerobic waterways. As the health of the land declines, so too does the health of the livestock and people dependent on livestock…

…Livestock as Part of the Solution.

Ruminants grazing in rangeland or cultivated forage agroecosystems are beneficial when they are appropriately managed (Delgado et al. 2011; Teague et al. 2013). Grazing ungulates play key ecological roles in grasslands and savannas, and can contribute positively to numerous ecosystem services. Beneficial effects could include increased water infiltration, improved water catchment, greater biodiversity, increased ecosystem stability and resilience, and improved C sequestration; all of which can help mitigate GHG emissions (DeRamus et al. 2003). When domestic ruminants are managed in a way that restores and enhances grassland ecosystem function, increased C stocks in the soil will lead to larger and more diverse populations of soil microbes, which in turn leads to greater C sequestration, including CH4oxidation (Bardgett and McAlister 1999; Teague et al. 2013; Jamali et al. 2014). With livestock management focused on building soil health, grazing animals can create C negative budgets, with more C entering the soil than is emitted indirectly or via ruminant emissions (Janzen 2010).Combining crop rotation with livestock grazing can be particularly effective at enhancing soil function and health (Delgado et al. 2011). Crop production can be managed to maintain permanent ground cover through the rotation of forage and row crop mixes, including cover crops, and legumes to increase soil fertility by fixing N. Grazing livestock can accelerate nutrient cycling through the consumption and decomposition of residual aboveground biomass. For example, sowing winter crops into permanent summer growing pastures and using crop rotation systems with forage crops and grazing animals have been shown to significantly reduce the damaging effects of many current arable land management practices, including soil erosion, loss of SOC, and elevated GHG emissions, especially where soil erosion potential is moderate to high (Delgado et al. 2011)….

…Conclusions

Soil is a depletable resource, but production of food for human consumption does not have to deplete the soil. Cropping and grazing practices that build SOC levels and soil microbial communities and functions, and that minimize soil erosion can result in soils being a net sink for GHGs rather than a major source of GHGs, as is currently the case. Effective soil management provides the greatest potential for achieving sustainable use of agricultural land under a rapidly changing climate. Ruminant livestock are an important tool for achieving sustainable agriculture. With appropriate grazing management, ruminant livestock can increase C sequestered in the soil to more than offset their GHG emissions, and can support and improve other essential ecosystem services for local populations. Affected ecosystem services include water infiltration, nutrient cycling, soil formation, C sequestration, biodiversity, and wildlife habitat. Our assessment suggests that increasing SOC globally within food production systems will reduce the C footprint of agriculture much more than reducing domesticated ruminant numbers in an effort to reduce enteric GHG emissions. The simultaneous increase in production of agricultural goods indicates that integrating livestock into mixed agricultural systems and grazing management to increase SOC, biodiversity, and soil quality would enhance resilience of soil and agroecosystems against climate change and extreme events.

A primary challenge to the increasing global demand for food is how to increase the scale of adoption of land management practices documented to have a positive effect on soil health. It is essential that scientists partner with environmentally progressive managers at sufficiently large scales to convert experimental data on managed landscapes into sound environmental, social, and economic results that will provide regional and global benefits. Rather than reducing ruminants and encouraging destructive agricultural land use by providing price subsidies and other subsidies, rewarding regenerative agricultural practices that focus on increasing soil C and that lead to greater adoption by land managers is essential to creating a robust, resilient, and regenerative global food production system.

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